I'm pretty new to a lot of robots and electronics engineering. I'm still working on understanding power with the Arduino, and because I don't want to toast any of my components I'm treading lightly. I just want to confirm that the motor shield from Adafruit will power the robot chassis w/ gearbox I was looking at purchasing:

Pololu Round Robot Chassis: http://www.robotshop.com/pololu-round-robot-chassis-kit-solid-blue-3.html(Yes, not direct from Pololu, since they only sell one with a serial server controller that I'm not interested in)Adafruit motor shield: http://www.adafruit.com/index.php?main_page=product_info&cPath=17_21&products_id=81

I will be hooking up a batter to the DC terminal on the Ardunio to power it, and will be plugging in another back -- type/size to be determined -- into the DC terminals on the motor shield. I don't want to even consider running the Arduino and motors off the same supply.

In the end, I want to build a basic robot -- at first it will just do a routine, then maybe follow lines, then I'll start playing with sensors and RC stuff. I think this platform will give me a good start. If anyone has a better suggestion for a chassis, please let me know. It's either this one or the 2WD chassis from DFRobot.

The motors in the Tamiya gearbox are 3 volt motors. The adafruit motor shield is specced for 4.5+ volt operation. You can run the Tamiya motors at 4.5 volts, but it will reduce their lifetime. There are 4.5 volt + motors available that are a direct swap for the Tamiya motors, but they have higher current ratings than the Adafruit motor shield:

Unfortunately, the only motor driver I'm familiar with made specifically to drive these Tamiya gearboxes is the Pololu serial driver that you said you weren't interested in. That's not to say there aren't others out there, but I'm not aware of any.

I wasn't very interested in the serial controller because I was hoping to go with a shield for the Arduino, just keeping things all in one neat little stack and (I think) easier to move to other projects in the future. There is the Ardumoto shield from SparkFun (http://www.sparkfun.com/products/9815) but I can't find any specs on it. The little quick start guide talks about 1-2A motors, so that may work?

That shield does have the current capacity for the Tamiya motors, but it's still limited on the minimum voltage it can drive the motors at. If you're dead set, you can run the Tamiya motors at 5 volts, they'll just have a shorter lifetime, maybe 10-20 hours roughly total runtime. Just order a set of RM3 motors to replace them with when they do give out and you'll be good to go. When I bought RM3 motors from Robotshop last summer, it took about 8 weeks to get them. They can be a long lead time item (and they're currently showing a 1-3 week lead time right now), but it's much easier finding motor drivers that work with them.

The Tamiya motors really are an oddball motor, combining low voltage with relatively high current (1.5-3V with a 2.1A stall current).